Eicosanoids, such as prostaglandin, thromboxanes, and leukotrienes, are one of the families of metabolites of arachidonic acid. To maintain homeostasis of the living body, eicosanoids show various physiological effects (see “Koza prostaglandin 1–8”, Makoto Katori, Seiitsu Murota, Shozo Yamamoto Ed. (1988)). These physiological effects purportedly appear through a specific cell membrane receptor of each eicosanoid. Leukotrienes, one of the eicosanoids, are a series of physiologically active lipids that show a strong physiological activity at low concentrations among the metabolites of arachidonic acid in the 5-lipoxygenase pathway (Samuelsson, B. et al. (1987) Science. 237, 1171–1176).
Leukotrienes are divided roughly into two kinds, namely leukotriene B4 (LTB4) and the peptide leukotriene in which peptides are bound to fatty acids. Leukotriene C4 (LTC4), leukotriene D4 (LTD4), and leukotriene E4 (LTE4) are examples of the latter peptide leukotrienes. The LTB4 is a strong activator of leukocytes, and plays important roles in inflammatory immune reaction, infection protection, and the like (Chen, X. S. et al. (1994) Nature 372. p179–182). On the other hand, LTC4, LTD4, and LTE4 have actions such as contraction of various smooth muscles (including the airway smooth muscle) stimulation of the mucos secretion in the airway, constriction of arteriolae and venule, and edudation of plasma protein (Taylor, G. W. et al. (1986) Trends Pharmacol. Sci. 7, p100–103). Therefore, it is thought that the peptide leukotriene is involved in the crisis, ingravescent, exacerbation of inflammation and allergic symptoms, for instance, respiratory diseases such as asthma, bronchitis, and allergic rhinitis, dermatosis such as psoriasis and dermatitis, and intestinal diseases such as inflammatory bowel disease and ulcerative colitis (Makoto Katori, Seiitsu Murota, Shozo Yamamoto Ed. (1988) “Koza prostaglandin 3”, 225–227, 484–486; Piper, P. J. et al., (1984) Physiol. Rev. 64. 744–761; Taylor, G. W. et al. (1986) Trends Pharmacol. Sci. 7. 100–103; Lewis, R. A. et al. (1990) N. Engl. J. Med. 323. 654–655). Moreover, it is known that the peptide leukotrienes, LTC4 and LTD4, cause a prominent decrease in cardiac contractivity and the coronary flow (Makoto Katori, Seiitsu Murota, Shozo Yamamoto Ed. (1988) “Koza prostaglandin 2”, 64–70; Piper, P. J. et al. (1984) Physiol Rev. 64. 744–761; Letts, L. G. et al., (1982) Br. J. Pharmacol. 76, 169–176; Chiono, M. et al., (1991) J. Pharmacol. Exp. Ther. 256, 1042–1048), and thus the relation of peptide leucotriene to cardiovascular disturbance is pointed out.
Taken together, it is thought that clarifying the structure and the characteristics of the receptor of leukotrienes would lead to elucidation of the physiological role of leukotrienes, and consequently, to elucidation of diseases related to leukotrienes, discovery of methods of medical treatment, and so on.
To date, according to the IUPHAR (International union of Pharmacology), receptors of leukotrienes are classified pharmacologically into three types, namely the BLT receptor, CysLT1 receptor, and CysLT2 receptor, (Alexander, S. P. H. et al., (1997) Trends Pharmacol. Sci. (Suppl.) 50–51).
The BLT receptor specifically recognizes the LTB4. The CysLT1 receptor and CysLT2 receptor both recognize peptide leukotrienes. The biological action of the CysLT2 receptor is not blocked by existing classical LTD4 receptor antagonists (ICI204219, MK476, SR2640, SKF104353, and LY170680, etc.) while that of the CysLT1 receptor is. The existence of additional peptide leukotriene receptor, apart from the CysLT1 receptor and the CysLT2 receptor, has been proposed (Jonsson, E. W. et al. (1998) Eur. J. Pharmacol. 357, 203–211).
The BLT receptor genes have been isolated and identified in both human (Yokomizo, T. et al. (1997) Nature 387. 620–624) and mouse (Martin, V. et al. (1999) J. Biol. Chem. 274. 8597–8603). Likewise, human CysLT1 receptor has been recently isolated and identified, and it turned out that LTD4 is a high affinity ligand thereto (Lynch, K. R. et al. (1999) Nature 399, 789–793). However, receptors of peptide leukotrienes, especially genes of receptors with a high affinity to LTC4 other than the CysLT1 receptor, have not been isolated and identified in any species until now.
In addition, antagonists of the BLT receptor (Negro, J. M. et al. (1997) Allergol. Immunopathol. Madr. 25, 104–112; Kishikawa, K. et al. (1995) Adv. Prostaglandin Thromboxane Leukot Res. 23, 279–281) and antagonists of the CysLT1 receptor (Leff, J. A. et al. (1998) N. Engl. J. Med. 339, 147–152; Suisa, S. et al. (1997) Amm. Int. Med. 126, 177–183; Grossman, J. et al. (1997) J. Asthma 34, 321–328) have been researched and developed, aiming at antiphlogistic drug.
On the other hand, among the leukotriene receptors, research and development of antagonists and agonists of the receptors with a high affinity especially to LTC4 has been remained behind (Gardiner, P. J. et al. (1994) Adv. Prostaglandin Thromboxane Leukot. Res. 22, 49–61; Capra, V. et al. (1998) Mol. Pharmacol. 53, 750–758). The main cause is that the binding of LTC4 to the receptor is masked by low affinity-LTC4 binding proteins, such as glutathione S-transferase and LTC4 synthase, which exist in cells and the tissues, so that binding experiments using cells and tissue preparations are difficult to conduct. Therefore, provision of a LTC4 receptor which enables binding experiments to be performed in vitro is needed in the art.